Scenario of the 1996 Volcanic Tsunamis in Karymskoye Lake, Kamchatka, T Inferred from X-Ray Tomography of Heavy Minerals in Tsunami Deposits
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Marine Geology 396 (2018) 160–170 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margo Scenario of the 1996 volcanic tsunamis in Karymskoye Lake, Kamchatka, T inferred from X-ray tomography of heavy minerals in tsunami deposits ⁎ Simon Falvarda, Raphaël Parisa, , Marina Belousovab, Alexander Belousovb, Thomas Giachettic, Stéphanie Cuvend a Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France b Institute of Volcanology and Seismology, Petropavlosk-Kamchatsky, Russia c Department of Earth Sciences, University of Oregon, Eugene, USA. d IODP-France, 14 Av. Edouard Belin, 31400 Toulouse, France. ARTICLE INFO ABSTRACT Keywords: The concentration and distribution of heavy minerals in tsunami deposits is not random and mostly source- Tsunami dependent. Heavy minerals may thus be good indicators of sediment provenance and tsunami flow dynamics. Phreato-magmatic eruption The tsunamis generated by the 1996 phreato-magmatic eruption in Karymskoye Lake represent a relevant case- Heavy minerals study because the provenance of the abundant heavy minerals found in the tsunami deposits is well constrained X-ray tomography (the on-going basaltic eruption itself). X-ray computed tomography (X-CT) of cores of tsunami sediments is used Karymskoye Lake to identify heavy minerals and characterise their source and spatial distribution in the tsunami deposit, and to propose a scenario of the coupled eruption and tsunamis. An original combination of methods including X-CT, SEM and XRF core scanner allows distinguishing subunits corresponding to pulses of sediments deposition and associated inputs of heavy minerals, together with erosive contacts, laminations, and rip-up clasts of the substratum. The structure of the tsunami deposits suggests that a major tsunami consisting of two main waves inundated the coastal terrace up to 100 m inland on the eastern shore of the lake; a scenario that is consistent with waves generated by experimental explosions. This largest tsunami might have occurred when underwater explosions were at a critical water depth of 40 m (corresponding to a two-third submerged explosion in the 60 m deep lake). However, more investigations are needed to better understand the critical conditions leading to a tsunami during underwater eruptions. 1. Introduction concentrations occurred towards the upper part of the 2004 tsunami deposits in Thailand, with mica flakes found more commonly in the Heavy minerals in clastic sediments and sedimentary rocks are finest-grained sediment samples. However, the 2011 Tohoku-oki tsu- commonly used to study diagenesis, weathering processes, sediment nami deposits in Sendai, which are particularly rich in heavy minerals, provenance, depositional processes, and to reconstruct paleoenviron- show no different assemblage compared to other pre-tsunami sediments ments (e.g. Dill, 1998; Mange and Wright, 2007). Heavy minerals are and no vertical trends with a 1 cm-interval sampling (Jagodziński et al., often reported in tsunami deposits (e.g. Switzer et al., 2005, 2012; 2012). Predominance of local sediments (beach, dune, soil) upon Bahlburg and Weiss, 2006; Szczuciński et al., 2006; Babu et al., 2007; offshore sediments is confirmed by the rarity of marine bioclasts in Morton et al., 2007, 2008; Narayana et al., 2007; Higman et al., 2008; the 2011 tsunami deposits at Sendai (Pilarczyk et al., 2012; Szczuciński Srinivasalu et al., 2008; Jagodziński et al., 2009, 2012; Moore et al., et al., 2012). 2011; Costa et al., 2015). A higher concentration of heavy minerals was The concentration and distribution of heavy minerals in tsunami estimated in tsunami deposits (Jagodziński et al., 2009) and post- deposits is mostly source-dependent, but they are promising indicators tsunami deposits (Babu et al., 2007) sediments, compared to pre- of sediment provenance and flow dynamics. Cuven et al. (2013) tsunami deposits. Heavy minerals described in recent tsunami deposits concluded that “further investigations are needed to improve under- are likely concentrated in pockets or laminae (e.g. Morton et al., 2007; standing of the spatial distribution of different populations of grains, in Higman et al., 2008; Srinivasalu et al., 2008; Jagodziński et al., 2012; terms of density and shape, and their relationship to sediment sorting in Switzer et al., 2012). Jagodziński et al. (2009) noted that higher mica tsunami deposits”. In this new contribution, X-ray tomography is used ⁎ Corresponding author. E-mail address: [email protected] (R. Paris). http://dx.doi.org/10.1016/j.margeo.2017.04.011 Received 28 October 2016; Received in revised form 21 April 2017; Accepted 23 April 2017 Available online 28 April 2017 0025-3227/ © 2017 Elsevier B.V. All rights reserved. S. Falvard et al. Marine Geology 396 (2018) 160–170 to (1) identify heavy minerals and characterise their source and spatial Akademii Nauk caldera to Karymsky stratovolcano, one of the most distribution in a tsunami deposit, and (2) to propose a scenario of the active volcanoes in Kamchatka. 1996 volcanic tsunamis in Karymskoye Lake (Kamchatka, Eastern After a strong earthquake on January 1st, 1996, there was an Siberia, Russia). This tsunami is a good candidate because the heavy intense seismic swarm and two eruptions started simultaneously from mineral population is mostly provided by the sublacustrine volcanic Karymskoye Lake and from the central vent of Karymsky volcano on eruption that generated the tsunami. The approach might give some January 2nd (Muravyev et al., 1998). Phreatomagmatic activity formed insights on the coupling between the eruption and the tsunami(s) and a new tuff-ring attached to the northern slope of the lake. The ice understanding of wave generation during phreatomagmatic eruptions. covering the lake might have prevented the generation of tsunami Volcanic tsunamis are generated by a variety of mechanisms, including waves during the first stages of the eruption. Pyroclastic base surges volcano-tectonic earthquakes, slope instabilities on volcano flanks, damaged bushes as far as 1.3 km from the vent in all directions, at pyroclastic flows, underwater explosions, shock waves, and caldera elevations up to 150 m above the level of the lake (Belousov and collapse (e.g. Paris, 2015). Among the historical record, volcanic Belousova, 2001). Ash fall deposits extend mostly to the southeast, with tsunamis represent a low-frequency hazard (about 5% of all recorded a thickness decreasing from 5 cm at 1.5 km from the vent to 1 cm tsunamis) but four events (Ritter Island 1888, Krakatau 1883, Unzen at > 3 km from the vent on the shores of the lake. Large ballistic blocks 1792, and Oshima-Oshima 1741) are ranked in the twenty deadliest of juvenile basalt, hydrothermally altered rocks and rhyodacitic pumice volcanic disasters (Auker et al., 2013). were ejected (Grib, 1998; Belousov and Belousova, 2001). Observation of empty bomb sags in September 1996 was interpreted as an evidence 2. The 1996 eruption and tsunamis in Karymskoye Lake of ice blocks ejected during initial explosions (Belousov and Belousova, 2001). Karymskoye Lake fills the late Pleistocene Akademii Nauk caldera, Tsunamis generated by underwater explosions were observed dur- fl fl the later belonging to the Eastern Volcanic Belt of Kamchatka ing helicopter ight and periodically triggered debris ows in the Peninsula. The lake is 4 km across, with steep flanks and a flat bottom Karymskaya River (Muravyev et al., 1998). Belousov and Belousova 3 ff at 60–65 m deep (Fig. 1). This ~0.5 km volume of fresh water is fed by (2001) described the e ects of the tsunamis on the shores of the lake, several streams and hot springs, and drained by the Karymskaya River and Belousov et al. (2000) estimated wave runups. The values of runup to the North (Belousov and Belousova, 2001). The post-caldera volcanic decrease with the distance from the source, i.e. the eruptive vent, with a history is poorly documented and apparently limited to scoria cones maximum runup of 19 m on the north-western shore (< 1 km from the and tuff rings on the northern shores of the lake (Belousov et al., 1997). vent) and a minimum runup of 1.8 m on the south-eastern shore (3 km ff 3 Eruptive vents are aligned along a North-South fault linking the from the vent). Boulders of volcanic tu up to 1.3 m were transported Fig. 1. Location map of Karymskoye Lake, Kamchatka Peninsula, Russia. Reconstructed pre-eruption bathymetric contours (modified from Torsvik et al., 2010) are in meters below the surface of the lake (black bold line at 624 m a.s.l.). Red circle indicates the location of the tuff-ring formed during the 1996 eruption. Deposits of the 1996 tsunami were studied all around the lake (black squares), and the sections sampled for X-ray tomography are indicated by yellow squares (K02 and K08). Geographical coordinates in decimal degrees. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 161 S. Falvard et al. Marine Geology 396 (2018) 160–170 Fig. 2. Effects of the 1996 eruption and tsunamis on the northern shore of Lake Karymskoye. Note the formation of a new tuff-ring with an inner diameter of 500 m, extensive destruction of the vegetation (bush) and erosion of the shoreline, formation of new beaches, and slope erosion near the eruptive vent. Modified from Paris (2015). Photograph showing the volcanic ash plume generated by one of the phreatomagmatic explosions (courtesy of Ya. D. Muravyev). up to 60 m inland. Soil erosion by successive tsunamis led to the underwater explosion of 5 × 1014 J generating a water cavity with a formation of talus up to 2–3 m high all around the lake, except on the diameter of 350 m and an initial surface displacement of 55 m can southern rocky shore. Sediment reworked by tsunami waves left new explain the observed runups of the largest tsunami.